1. Field of the Invention
The invention relates to a high voltage metal-oxide-semiconductor (hereinafter abbreviated as HV MOS) device, and more particularly, to a high voltage lateral double-diffused metal-oxide-semiconductor (HV-LDMOS) device.
2. Description of the Prior Art
Double-diffused MOS (DMOS) transistor devices have drawn much attention in power devices having high voltage capability. The conventional DMOS transistor devices are categorized into vertical double-diffused MOS (VDMOS) transistor devices and lateral double-diffused MOS (LDMOS) transistor devices. Having advantages of higher operational bandwidth, higher operational efficiency, and convenience to be integrated with other integrated circuit due to its planar structure, LDMOS transistor devices are prevalently used in high operational voltage environments, such as CPU power supplies, power management systems, AC/DC converters, and high-power or high frequency (HF) band power amplifiers. The essential feature of LDMOS transistor devices is a lateral-diffused drift region with low dope concentration and large area. The drift region is used to alleviate the high voltage between the drain and the source; therefore the LDMOS transistor device can have higher breakdown voltage.
It is well-known that characteristics of high element density and high breakdown voltage are always required for the HV MOS transistor device. However, breakdown voltage and element density are conflicting parameters with a trade-off relationship. Therefore, a HV LDMOS transistor device that is able to realize high breakdown voltage but without decreasing the element density is still needed.